5 weeks 4 days sac but no baby?

This scan isn’t mine but using it as an example what mine looked like. On Monday I went in for a scan they saw a very tiny sac measuring 4 weeks and 6 days. 3 days later went back in for another scan I’m supposed to be 5 weeks and 4 days now but was messaging 6 weeks but I ain’t ) weeks but there was just a sac the sac as grown in the past 3 days but there’s only a scan no yolk no baby at all. I took a digital when I got it says 3+ it said 2-3 last Tuesday so it gone up. Should I be worried so worried!